In a Class-D amplifier including two switching transistors to constitute a push-pull circuit, shoot-through current is generated when the two switching transistors simultaneously turn into a conduction state (hereinafter, a conduction state is referred to as “on” and a non-conduction state is referred to as “off”). The class-D amplifier is supplied with a time span during which the two switching transistors are not simultaneously turned on (hereinafter referred to as a “dead time”) within a switching period of the two transistors (one switching from on to off and the other switching from off to on) to suppress generation of shoot-through current.
Meanwhile, in the class-D amplifier, there is a possibility that a distortion due to the dead time occurs and sound quality is deteriorated when audio signal is amplified. Thus, it is preferable that the dead time be set as short as possible. However, in many cases, the generation of a distortion does not cause any problem while no sound is emitted from a loudspeaker connected to the class-D amplifier owing to no audio signal to be amplified or because of the mute setting of sound emitted from an audio playback apparatus equipped with the class-D amplifier, for example.
There is a presented class-D amplifier in which dead time is extended relatively to suppress shoot-through current while no sound is emitted from the loudspeaker. Specifically, the class-D amplifier increases the capacity of capacitor (or the number of capacitors) used in a resistor-capacitor (RC) circuit included in a dead time generator for generating the dead time by switch operation, and increases the time constant, thereby the dead time is extended while no sound is emitted from the loudspeaker. PTL 1 discloses an art related to these class-D amplifiers.